1. Field of the Invention
This invention relates to a molding machine which continuously carries out a series of operations including injection molding of a parison, temperature control, and stretch blow molding of thin-walled containers such as bottles, cups, and the like.
2. Description of the Prior Art
An injection stretch blow molding machine disclosed in U.S. Pat. No. 4,105,391 has a rotary disk disposed on the undersurface of a base plate provided above a machine bed. The rotary disk transfers a parison and a molded product. This rotary disk is supported by a central rotary shaft connected to a driving device on the base plate and the peripheral edge of the base plate to thereby eliminate the provision of a central column which is essential to the molding machine as disclosed in U.S. Pat. No. 2,331,687.
No obstacle is therefor present between the machine bed and the base plate thereabove due to the omission of the central column, and a space formed thereat may be effectively used as a working space necessary for injection stretching blow molding. As a consequence, the aforesaid molding machine is smaller than a molding machine having a central column. Therefore, incorporation of various devices necessary for molding is made easy and moreover all the steps from injection molding of a parison to releasing of a molded product can be carried out under one and the same base plate.
With this, management of molding steps becomes easy, the molding cycle time is shortened, and thin-wall containers such as bottles, cups, etc. having uniform wall-thickness distribution may be produced in volume. However, in the aforementioned conventional molding machine, the base plate is supported only by the peripheral edge since the central column is omitted. If the diameter of the rotary disk is increased to accommodate a greater number of neck molds on the undersurface for volume production or if the wall thickness of the base plate in the injection operating stage is increased to effect high pressure clamping, the central portion of the base plate bends and this sometimes interferes with the horizontal rotation of the rotary disk.
Furthermore, since the mold clamping device provided at right angles to the base plate is arranged so that the injection mold may be positioned under the rotary disk, the mold clamping device cannot be guided by four tie bars, as in a conventional injection molding machine, and the position of the tie bars will be set externally of the rotary disk. In addition, the number and location of the tie bars is restricted to only opposite sides. Therefore, the guiding the mold clamping device is liable to be unstable, and moreover the clamping force is restricted. Many other problems arise as well.
These problems may be solved by increasing the number of support points for the base plate and of the tie bars. However, in the conventional construction wherein the rotary disk is held on the undersurface of the base plate, the number and location of support points is limited to only the peripheral edge. This makes it difficult to provide for the support in the central portion where it would be most effective with respect to the bending resulting from loads, and in addition, leaving no room for the increase of the tie bars.